1. Field of the Invention
The invention relates to polymeric transition metal catalysts, to processes for preparing them, to intermediates and also to the use of the transition metal catalysts as catalysts in organic reactions, in particular in olefin metathesis reactions.
2. Brief Description of the Prior Art
Olefin metathesis reactions, for example ring-closing metathesis (RCM), cross-metathesis (CM) and ring-opening metathesis polymerizations (ROMP), are important synthetic methods for forming C—C bonds.
For olefin metathesis reactions, a multiplicity of catalyst systems has been developed, which are described in summary, for example, in T. M. Trnka, R. H. Grubbs, Acc. Chem. Res. 2001, 34, 18-29.
With regard to activity, those catalyst systems which comprise alkoxybenzylidene complexes of transition metals in particular have proven useful. However, the removal and, if possible, the reuse of catalysts is becoming more important, since catalyst metal residues in the product may considerably impair its quality.
For example, Veldhuizen et al., J. Am. Chem. Soc. 2002, 124, 4954-4955 disclose phosphine-alkoxybenzylidene complexes of ruthenium which are suitable as reusable catalysts for the cross-metathesis of tricyclic norbornenes. However, this restriction to specific substrates is a hindrance to industrial use.
Gessler et al., Tetrahedron Lett. 41, 2000, 9973-9976 also describe stable ruthenium complexes which contain dihydroimidazol-2-ylidene and isopropoxybenzylidene ligands. However, the difficult recovery of the catalyst is not satisfactory for industrial applications.
WO 02/14376 A2 describes dendrimeric ruthenium complexes which have dihydroimidazol-2-ylidene and isopropoxybenzylidene ligands and can advantageously be removed from the reaction products in the catalytic reaction mixtures which result from olefin metathesis reactions. However, a disadvantage of these catalysts is the complicated synthesis of the dendritic framework.
There was therefore still a need for easily obtainable catalysts which have high activity even on reuse and can easily be removed from the catalytic reaction mixtures.